Esters of glycolic acid



Patented July 14, 1942 ESTERS OF GLYCOLIG ACID Donald J.Loder,Wilmington, and Wilber 0. Teeters, Roselle, Del., assignors to E. I. duPont de Nemours & Company, Wilmington, Del, a

corporation of Delaware No Drawing. Application May 6, 1939,

' Serial No. 272,134

8 Claims.

The present invention relates to new materials and to methods for theirpreparation, and more particularly, to the polyhydric alcohol esters ofhydroxy and alkoxy substituted acetic acids and l methods for theirpreparation.

An object of the present invention is to provide new compositions ofmatter and processes for their preparation. A further object of theinvention is to provide monoand poly-ethylene glycol and monoand(ii-glycerol and triglyceryl esters of glycolic and substituted glycolicacids, together With processes for their preparation. Yet another-objectof the invention is to provide a process for the preparation of glycolmonoand di-glycolates and glycerol monoand diglycolates by esterifyingglycolic acid with glycols and glycerol, respectively. A further objectof the invention is to provide a process for the preparation of glycolglycolates, glycerol glycolates, or a glyceryl glycolate which comprisesreacting a glycolide with glycols or glycerol. and advantages of theinvention will hereinafter appear.

These objects, as well as others which will be apparent as thedescription proceeds, may be accomplished by reacting a lower alkylester of an orry-substituted acetic acid with a polyhydric alcohol underconditions favorable to the interchange of alcohol radicals. Thisinterchange of alcohol radicals is effected by heating the alcohol andester together, preferably in the presence of alkaline alcoholysiscatalysts, The ester interchange proceeds more readily if the alcoholselected for reaction with the ester boils at a higher temperature thanthe alcohol liberated by the interchange, because the latter alcohol isthen more readily removed from the zone of reaction, for example, bydistillation.

The ester interchange process described above may be employed for thepreparation of either the monoglycolates or the polyglycolates, forexample, when it is desired to prepare ethylene glycol monoglycolate, inaccord with the ester interchange process, equimolecular proportions ofthe ester and ethylene glycol are reacted. If, on the other hand, thereaction mixture contains two moles of the ester per mole of theethylene glycol and the reaction continues to completion, the productwill be ethylene glycol diglycolate. In like manner, if it is desired toobtain a glycerol monoand di-glycolate or glyceryl tri-glycolate, onemole of glycerol is reacted with one, two, or three moles of an ester ofglycolic acid. The process is applicable generally to the preparation ofpolyhydric alcohol, monoand polyglycolates, monoand poly-alkoxyglycolates and monoand poly-alkoxy methoxy glycolates from thepolyhydric alcohols and the lower alkyl esters of, respectively,glycolic acid, CH2(OH)COOH, alkoxy acetic acids, CH2(OR)COOH, such asOther objectsmethoxy acetic acid, CH2(OCH3)COOH, and alkoxy methoxyacetic acids, CH2(OCH2OR) COQH, such as. methoxy methoxy acetic acid,CH2(OCH2OCH3)'COOH. The methyl, ethyl, propyl, isopropyl, butyl,isobutyl, amyl, etc. esters of this acid, may be reacted with thepolyhydric alcohols generally, such, for example, as: the glycols, e.g., ethylene glycol, propylene glycol, butylene glycol, amylene glycol,diethylene glycol, trimethylene glycol, octadecanediol, tetramethyleneglycol, hexamethylene glycol, or the alcohols containing more than twohydroxyl groups, such as glycerol, diglycerol, triglycerol, trimethylolmethane and trimethylol propane; sugar, such as, dextrose; sucrose,Xylose, galactose, fructose, maltose, and mannose; and the sugaralcohols, such as, sorbitol,'mannitol, and dulcitol; as well as castoroil (glyceryl trlricinoleate), hydrogenated castor oil, (hydroxystearin) and like long chain polyhydric alcohols.

This invention likewise includes esters of glycolic acid, alkoxyandalkoxy methoxy-acetic acids with ether'alcohols, i. e., polyhydricalcohols having at least one free hydroxyl group, one or more hydroxylgroups being etherified. Examples of such ether alcohols include thernonoalkyl ethers of ethylene glycol, such as the mono-methyl, -ethyl,-propyl or -butyl ethers of ethylene glycol, propylene glycol, etc.Esters of this class would be, e. g., ethylene glycol monomethyl etherglycolate, ethylene glycol mono-ethyl ether glycolate, ethylene glycolmonomethyl ether methoxy acetate,

CH2 (0cm) COOCHzCI-IzOCHs and ethylene glycol monomethyl ether methoxymethoxy acetate,

. CH2(OCH2OCH3) COOCHzCI-IzOCHs The monoand di-glycolates of themonoglycerides are likewise included, e. g., the monoglycolates of themonoglycerides,

' CH2 OH) COOCH2CHOH.CH2OOCR in which R is methyl, ethyl, propyl, butyl,etc.

butoxy-acetic acids, etc.; the alkoxy alkoxy acetic acids, CH2(OROR)COOH, e. g., ethoxy methoxy-, propoxy methoxy-, isobutoxy methoxyaceticacids, etc.; and the alkoxy carbomethoxy methoxy acetic acid,

CH2 (OCHZQCHzCOOR) COOH e. g., methoxy carbomethoxy methoxy acetic acidor ethoxy carbomethoxy 'methoxy acetic acid, which may be prepared byreacting glycolic acid formals with carbon monoxide in accord with theprocess described in the copending application S. N. 256,854, filedFebruary 17, 1939.

The esters of the present invention are preferably prepared by the abovedescribed ester interchange process, for the reason that this processprovides ,a means of obtaining both the monoand poly-glycolates inexcellent purity and yield. Simple esterification may be employed,however, that is, by the interaction of the polyhydric alcohol with theglycolic acid. There appears to be one exception to this, in that, dueto the dehydrating characteristics of glycolic acid, it does not reactreadily with glycerol but forms acrolein at the expense of the glycerolester and, consequently, simple esterification should preferably not beemployed when the glycerol esters of glycolic acid are desired.

. The invention likewise provides another ester interchange process forthe preparation of esters of glycolic acid. This process involves theinteraction of a polyhydric alcohol or ether alcohol with glycolide,which may be considered to be a poly-ester of glycolic acid. Thisreaction may be efiected by first forming the glycolide (prepared, e.g., in the usual manner by heating the glycolic acid to drive ofi allthe water), and subsequently reacting the glycolide (which may bepresent as a diglycolide, or as a polyglycolide) with the polyhydricalcohol. If a partially dehydrated glycolic acid is used, e. g., adiglycolide or polyglycolide in the presence of free glycolic acid, theinitial reaction is carried out under reflux and then water ofesterification, of free glycolic acid and glycol removed with the aid ofheat, either with or without a water carrier, such as, toluene.Ordinarily, this ester interchange may be conducted under atmosphericpressure, particularly with the higher boiling polyhydric alcohols,although if low boiling alcohols are employed, autogenous pressure orapplied pressures of from 5 to 600 atmospheres may be employed.

The more detailed practice of the invention is illustrated by thefollowing examples in which parts given are by weight unless otherwisestated. There are, of course, many forms of the invention other thanthese specific embodiments.

EXAMPLE I.-Ethylene glycol monoglycolate (A) To 2250 parts (25 moles) ofmethyl glycolate was added 1550 parts (25 moles) of ethylene glycol and,as catalyst, a solution of 3.0 grams of sodium in 7 grams of methanol(30% sodium methoxide solution). This mixture was refluxed under afractionating column, fitted with a distilling head arranged forcontrolled reflux, until the head temperature had receded to 6465 C. Themethanol was removed as rapidly as possible at the head of the column,the head temperature being carefully maintained between 64 C. and 66 C.The refluxing and the collecting of the methanol were continued forapproximately ten hours, at the end of which time approximately 800grams (25 moles) of methanol had been collected.

The heat was discontinued and any low boiling material which remainedwas removed by vacuum distillation. (If desired the color of the productmay be improved by treatment with 2 per cent. of its weight of astandard decolorizing charcoal.

For most purposes, however, the color of the untreated ester wassatisfactory.)

(B) To 310 parts (5 moles) of ethylene glycol, contained in a suitable3-necked flask equipped with an efficient stirrer and reflux condenser,was added 290 parts (5 moles) of powdered polyglycolide, prepared bycompletely dehydrating glycolic acid at elevated temperatures (-220"C.). The temperature of the reaction mixture was raised to and held at atemperature of 100- 200", preferably between -200 C., for a period ofapproximately five hours.

In both (A) and (B) the reaction mixture was cooled, and the productobtained was a pale amber-colored liquid which contained 98 to 99 percent. of glycol monoglycolate. The yield was substantially quantitative,based on either the glycol or glycolate; sp. gr. was 1,283 60 F./60 F.and the saponification number was 460.

EXAMPLE IL-Ethylene diglycolate The conditions and procedure are thesame as Example I.

Quantities:

Parts Moles Ethylene glycol 930 15 Methyl glycolate 2,700 30 Anhydrouspotassium carbonate (catalyst) -10 parts Methanol off 900 30 Product:

Yield quantitative. Amber colored viscous liquid. Sp. gr. 1.327/20/4.Sap. No. 611.

EXAMPLE III.-Glycerol monoglycolate The conditions and procedure are thesame as Example I.

Quantities:

Parts Moles Methyl glycolate 1,980 22 Glycerol (96%) 2,108 22 Anhydrouspotassium carbonate (catalyst)-l0 parts Methanol off 704 22 Product:

Yield quantitative. Pale amber colored liquid. Sp. gr. 1.320 60/60 F.Sap. No. 380.

EXAMPLE IV.GZ 1/cer0l diglycolate The conditions and procedure are thesame as Example I.

constants. Yield substantially quantitative in both cases. Amber coloredviscous liquid. Sp. gr. 1.393 20/4. Sap. No. 542.

' EXAMPLE V.-Beta-ethory ethyl glycolate 1 Up to and through the removalof methanol the conditions are the same as Example I.

Quantities:

Parts Moles Methyl glycolate 9.90 11 Beta-ethoxy ethanol (Cello solve)900 10 Catalyst: 1 part Na in 4 parts of methanol, anhydrous potassiumcarbonate-5 parts. Methanol ofl 39 9.7

EXAMPLE VL-Beta-methoxy ethyl glycolate To a mixture of 760 parts moles)of crystalline glycolic acid and 760 parts (10 moles) of beta-methoxyethanol was added 2 parts of concentrated sulfuric acid and 50 parts ofbenzene i (water carrier). The reaction mixture was heated to refluxtemperature and the water of esterificationQwhich separated as a lowerlayer in a suitable decanting type distilling head, was removed. Whenthe distillate no longer formed two layers the heat was discontinued andthe crude ester cooled. The acid catalyst present in the crude mixturewas exactly neutralized with anhydrous potassium carbonate and thebeta-methoxy ethyl glycolate distilled and recovered in a yield of 70 to80%. It was recovered as a mobile, colorless liquid having a B. P. of155-156/135 mm.; a sp. gr. of 1.163 60/60 F. and a saponification No, of417.

EXAMPLE VlI.0ctadeca1 tediol digylcolate The procedure was the same asin Example 1 with the following exceptions: isobutanol, instead ofmethanol, was distilled off at the head "of the column, at 105-110"; thereaction mixture was blanketed with nitrogen and a slow stream of thisgas was continuously passed over the surface during the esterinterchange; the pot temperature was held between 160-170 throughout thereaction; the product was filtered hot to give a quantitative yield ofthe ester.

Quantities Product:

White low melting solid. Sap. No. theoretical 194; found 184.

EXAMPLE VIII.Castor oil glycolate Procedure the same as foroctadecanediol diglycolate, Example VII.

Quantities:

Parts Moles Castor oil 888 1 Isobutyl glycolate 396 3 Sodium methoxide(catalyst)3.0 parts of 30% in methanol Product:

Yield substantially quantitative. Amber reddish viscous liquid. Sap. No.242.

EXAMPLE IX. Ethylene glycol monomethoxy acetate Procedure the same asExample I (glycol monoglycolate) with the exception that, after thereaction mixture was cooled, the alkaline catalyst was exactlyneutralized with sulfuric acid and the product distilled under reducedpressure.

Quantities:

Parts Moles Methyl methoxy acetate 260 2.5 Ethylene glycol 155 2.5Sodium methoxide (catalyst) (30% in methanol)2 parts Product:

Yield substantially quantitative, Colorless liquid. B. P. 141-142 C./25mm. Sp. gr, 1.174 60/60 F. Sap. No. 420,

EXAMPLE X.Ethylene bis-methoxy acetate Procedure same as for Example IX.Quantities:

Parts Moles Methyl methoxy acetate 520 5.0

Ethylene glycol 155 2.5 Sodium methoxide (catalyst) (30% in methanol)2parts Product:

Yield substantially quantitative. Colorless liquid. B. P. 176-77 C./25mm. Sp. gr. 1.194 60/60 F. Sap. No. 555.

The polyhydric alcohol esters and ether-esters of glycolic acid, as wellas the other esters de-- scribed herein, have many characteristics whichparticularly fit them for uses in the arts. They ,are all generallyuseful as solvents or plasticizers for many natural and synthetic resinswhich are used with or without pigments, fillers, extenders and thelike,which compositions are employed for the preparation of lacquers,pigments,

paste pigments, etc., 'or for the formation of films, filaments, rods,tubes, or shaped articles. More specifically, they are generally usefulas solvents, plasticizers and softeners for natural resins, such, forexample, as dammar, copal, kauri and for the synthetic resins such, forexample, as the alkyds; cumarone-indene; chlorinated diphenyl;

soluble types of polymerized hydrocarbons, phenol-formalde'hyde andurea-formaldehyde resins;

ester gum; polymeric acrylic and. methacrylic acids and their esters,amides, nitriles, imides, salts, interpolymers, and other derivatives;polyvinyl alcohol; the polyvinyl esters; styrene and other polymericresins, as well as simple mixtures of the natural and/or syntheticresins, and/or interpolymers of the polymeric resins.

The polyhydroxy alcohol esters of glycolic acid' are also useful assolvents, plasticizers or softeners of regenerated cellulose and thecellulose derivatives, such as, cellulose acetate, nitrate,acetonitrate, aceto-propionate,.methyl cellulose, ethyl cellulose andother organic derivatives of cellulose or mixtures thereof.

The polyhydric alcohol esters of glycolic acid are likewise generallyapplicable as the major ingredients in the preparation of printing padsand ink feeders of all types, as penetrating agents for printing pastes,and as major ingredients in the preparation of inks, both for theprinting of paper, textiles, wood, metal or other materials.

The ethylene glycol monoglycolate, diglycolate and glycerol mono-, diandtri-glycolate, may be used as softeners for glassine paper, as a.substitute for glycerine in tobacco, as a softener for regeneratedcellulose and as a substitute for glycerol in printing ink compositions.They have likewise been found acceptable for the sizing of theartificial and natural silks and particularly for the sizing ofregenerated cellulose filaments and fabrics and are also most effectiveas softening agents for cotton, wool, linen, jute, rayon and silk.

Glycolate esters of the alkyl ethers of polyhydric alcohols such, forexample, as glycolic acid esters of the mono-alkyl ethers of ethyleneglycol, HOCHzCOOCHzCHzOR, are, as has been generall'y stated above,excellent solvents for cellulose ethers and cellulose esters. Thesecompositions are especially valuable in brush-type lacquers and lacquersapplied hot, as they improve the fiow and gloss properties of the,resulting films. The ether-esters have been found acceptacle asfrothing agents for the flotation of ores andas solvents for theabsorption of acidic gases such as the sulfur oxides, hydrogen sulfides,etc. Furthermore, they, together with the other polyhydric alcoholesters of glycolic acid, are excellent solvents and liquid media forcertain dyestuffs and pigments wherein they may be substituted for theethers of the polyhydric alcohols.

The polyhydric alcohol esters and ether-esters of glycolic acids,hereinbefore described, may also be used as ingredients in thepreparation of compounds for defrosting and anti-misting; in cosmeticpreparations; as dye solvents for basic acid and direct dyes; as thefluid medium for electrolytic condensers; as ingredients in leatherfinishes and varnish removers; as solvents and fixatives for perfumes;as softeners for cork binders, glue, gelatin, paper and textile sizes;as an ingredient in dentifrice compositions; as softeners for casein,zein, soybean, protein plastics, etc.; as an ingredient in leak-proofingcompositions for gas distributing systems, gas masks and the like; inthe preparation of wetting, dispersing and penetrating agents, etc.,such as sulfates and the like; as precipitation inhibitors; and asingredients in fluids for hydraulically actuated mechanisms.

The phosphate derivatives of the polyhydric aicohol glycolates arelikewise useful as plasticizers generally for use in combination withthe aforementioned natural and synthetic resins, as well as thecellulose ethers, esters, and regenerated forms of cellulose.

The esters of the alkoxy acetic acids, in addition to the uses abovedescribed for the glycolic esters of the alkyl ethers of the polyhydricalcohols and because of their large number of active solvent groups, areparticularly excellent solvents for gases, liquids, solids and resins.The excellent solvent properties of materials of this type can beattributed to the combinadon of ether and ester groupings.

All glycolate esters disclosed can be reacted with an aliphatic oraromatic anhydride or acid to give relatively water insoluble estersthat are good plasticizer-softeners. As an example the glycerolglycolates reacted with acetic anhydride will give the triacetates ofthe three glycolates of glycerol.

From a consideration of the above specification it will be realized thatmany changes may be made in the details therein given without departingfrom the scope of the invention or sacrificing any of the advantagesthat may be derived therefrom.

We claim:

1. A process which comprises the alcoholysis of alkyl glycolate with apolyhydric alcohol.

2. A process which comprises the alcoholysis of methyl glycolate withethylene glycol to form an ethylene glycol glycolate.

3. A process which comprises the reparation of ethylene glycolmonoglycolate which comprises interacting a mixture containingsubstantially equimolar proportions of ethylene glycol and methylglycolate, whereby the methyl group is replaced by the ethylene glycolgroup.

4. Ethylene glycol monoglycolate having a specific gravity ofapproximately 1.28 at 60 F/60 F.

5. A process which comprises alcoholysis of an ester of anoxy-substituted acetic acid with a dihydric alcohol which boils higherthan the alcohol formed by the reaction.

6. A process which comprises alcoholysis of a. glycolic acid ester of alower aliphatic alcohol with a dihydric alcohol which boils higher thanthe alcohol formed by the reaction.

7. A process which comprises the alcoholysis of a lower alkyl ester ofglycolic acid with a dihydric alcohol that boils at a higher temperaturethan the alcohol liberated by the alcoholysis.

8. A process which comprises refluxing approximately equimolecularproportions of methyl glycolate and ethylene glycol in the presence ofsodium methoxide as the catalyst until head temperatures recede to fromapproximately 64 to 65 C. and subsequently removing the methanolsubstantially as rapidly as formed.

DONALD J. LODER. WILBER O. TEE'I'ERS.

